1. Field of the Invention
The present invention relates to a light source unit including a light source for emitting light used for thermally-assisted magnetic recording, and to a thermally-assisted magnetic recording head constituted by joining the light source unit and a slider. The present invention further relates to a method for manufacturing the light source unit.
2. Description of the Related Art
As the recording densities of magnetic recording apparatuses become higher, as represented by magnetic disk apparatuses, further improvement has been required in the performance of thin-film magnetic heads and magnetic recording media. The magnetic recording medium is generally a kind of discontinuous body of magnetic grains gathered together, and each of the magnetic grains has a single magnetic domain structure. Here, one record bit consists of a plurality of the magnetic grains. Therefore, in order to improve the recording density, it is necessary to decrease the size of the magnetic grains and reduce irregularity in the boundary of the record bit. However, the decrease in size of the magnetic grains raises a problem of degradation in thermal stability of the magnetization due to the decrease in volume.
As a measure against the thermal stability problem, it may be possible to increase the magnetic anisotropy energy KU of the magnetic grains. However, the increase in energy KU causes the increase in anisotropic magnetic field (coercive force) of the magnetic recording medium. Whereas, the intensity of write field generated from the thin-film magnetic head is limited almost by the amount of saturation magnetic flux density of the soft-magnetic material of which the magnetic core of the head is formed. As a result, the head cannot write data to the magnetic recording medium when the anisotropic magnetic field of the medium exceeds the write field limit.
Recently, as a method for solving the problem of thermal stability, so-called a thermally-assisted magnetic recording technique is proposed. In the technique, a magnetic recording medium formed of a magnetic material with a large energy KU is used so as to stabilize the magnetization, then anisotropic magnetic field of a portion of the medium, where data is to be written, is reduced by heating the portion; just after that, writing is performed by applying write field to the heated portion.
In this thermally-assisted magnetic recording technique, there has been generally used a method in which a magnetic recording medium is irradiated and thus heated with a light such as near-field light (NF-light). In this case, it is significantly important where and how a light source with a sufficiently high light output should be disposed inside a head in order to stably supply a light with a sufficiently high intensity at a desired position on the magnetic recording medium.
As for the setting of the light source, for example, U.S. Pat. No. 7,538,978 B2 discloses a configuration in which a laser unit including a laser diode is mounted on the back surface of a slider, and US Patent Publication No. 2008/0056073 A1 discloses a configuration in which a structure of a laser diode element with a monolithically integrated reflection mirror is mounted on the back surface of a slider. Further, US Patent Publication No. 2005/0213436 A1 discloses a structure of slider that is formed together with a semiconductor laser, and Robert E. Rottmayer et al. “Heat-Assisted Magnetic Recording” IEEE TRANSACTIONS ON MAGNETICS, Vol. 42, No. 10, p. 2417-2421 (2006) discloses a configuration in which a diffraction grating is irradiated with a light generated from a laser unit provided within a drive apparatus.
Furthermore, the present inventors propose a thermally-assisted magnetic recording head with a “composite slider structure” which is constituted by joining a light source unit provided with a light source to the end surface (back surface) of a slider provided with a write head element, the end surface being opposite to the opposed-to-medium surface of the slider. The “composite slider structure” is disclosed in, for example, US Patent Publication No. 2008/043360 A1 and US Patent Publication No. 2009/052078 A1.
While various forms of installation of a light source have been proposed, all of the laser diodes described above are devices made of a semiconductor. Outputs of semiconductor devices vary in response to changes in ambient temperature. In particular, ambient temperatures that are assumed in environments in which magnetic disk apparatuses are used are in the range of −5 to 60° C., for example. Accordingly, the range of variations of light output from the light source provided in a head should be estimated to be considerably wide. In addition, since changes in temperature of the light source due to heat radiated from surrounding elements and the light source itself are also considerably large, the range of variations in light output from the light source further widens. Therefore, in order to stably provide output light with a constant intensity at different temperatures, measures should be taken to detect changes in light output from the light source in real time and to keep the light output from the light source constant.
However, it is difficult to install a system for monitoring the light in an element-integration surface of a head for thermal assist together with an optical system that propagates the light for thermal assist, because of a limited area of the element-integration surface. In practice, femto sliders are commonly used as head slider substrates. The area of the element-integration surface of the femto slider is as small as 230 micrometers (μm)×700 μm. In these circumstances, little has been done to monitor light output from the light source for thermal assist.